This invention relates to an apparatus which receives packets belonging to different frames of various origins, carried in interlaced form by an incoming asynchronous time-division multiplex, groups the packets of each frame together and retransmits the reconstructed frames in serial form over a single outgoing transmission medium.
The packets are all of the same length and are carried in the incoming asynchronous time-division multiplex. A frame consists of packets concerning a given communication link, of any length defined as a number of bits. The packets of a given link are identified by a label which is included in the packet header. The first and last packets of an incoming frame comprise an open-frame and end-frame flag respectively. The frame format can comply with the HDLC standard. Transmission of a frame over the outgoing transmission medium consists in serial transmission of all the bits of the frame, in the same order as their order of arrival in the apparatus. Aligned flags are inserted between the reconstructed frames.
The problem of reconstructing frames such as this was raised in the study project called PRELUDE, conducted by the French Post and Telecom authorities in connection with a wideband asynchronous time-division digital network (RTA). In particular, it is necessary to reconstruct frames in the local switching exchanges of the RTA network and in bridges between the RTA network and synchronous packet transmission networks, such as TRANSPAC.
For example, an apparatus according to the invention, included in an asynchronous local time-division switching exchange would recompose the signalling frames from the incoming signalling packets in order to transmit the reconstructed frames to a signalling node ensuring their processing. In an asynchronous time-division exchange, all the incoming signalling packets converge on one or more signalling queues. The apparatus is connected to the input of a signalling queue and receives the incoming signalling packets delivered by the queue.
In addition, an asynchronous time-division network must, at least during the installation transition phase, live side by side with existing synchronous packet transmission networks such as TRANSPAC. In other words, it must be possible to establish data links between terminals connected to the asynchronous time-division network and terminals connected to Transpac type networks. Passage from one network to another is by bridges. In the direction of transmission from asynchronous time-division network to Transpac type network, the function of the apparatus according to the invention is to reconstruct the frames from the packets delivered by the asynchronous time-division network, before they are processed by a bridge.